In the deployment of a prosthesis such as a stent or stent graft into the human or animal body via intraluminal techniques, an introducer or delivery device is used to introduce the prosthesis into a vessel or a lumen of the body. After the prosthesis has been deployed and expanded within the lumen, the introducer is withdrawn from the body.
Stents may be inserted into an anatomical vessel or duct for various purposes. Stents may maintain or restore patency in a formerly blocked or constricted passageway, for example, following a balloon angioplasty procedure. Other stents may be used for different procedures. For example, stents placed in or about a graft have been used to hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be either self-expanding or balloon-expandable, or they may have characteristics of both types of stents. Self-expanding stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires, and/or releasing diameter reducing ties. With self-expanding stents, the stents expand primarily based on their own expansive force without the need for further mechanical expansion. In a stent made of a shape memory alloy such as nitinol, the shape memory alloy may be employed to cause the stent to return to a predetermined configuration upon removal of the sheath or other device maintaining the stent in its pre-deployment configuration.
When trigger wires are used as a deployment control mechanism, the trigger wires may releasably couple the proximal and/or distal ends of a stent or stent graft to a delivery catheter. Typically, one or more trigger wires are looped through a portion of the stent near a vertex of the stent. For example, trigger wires may be used to restrain a Z-stent or Gianturco stent formed of a series of substantially straight segments interconnected by a series of bent segments. The trigger wires may be disposed through, and pull upon, the bent segments to pull the stent closely against the delivery catheter. Trigger wires also may be used in conjunction with different stent designs such as cannula-cut stents having acute or pointed bends. In such examples, the trigger wires may be looped around one or more vertices formed beneath the proximal and/or distal apices, for example, at a location where an individual apex splits into two separate strut segments. Any of the stents may have barbs and/or other anchoring members to help decrease prosthesis migration.
One form of introducer uses a proximal nose cone with a distally facing capsule to encompass an exposed stent and barbs on the exposed stent of a stent graft during introduction. After the stent graft has been released and the capsule has been removed from the exposed stent, the capsule, along with the introducer, is withdrawn from the body. The capsule, however, has a distally facing opening with a surrounding edge. This edge may engage with stents of the just introduced stent graft and dislodge the stent graft from its position on the wall of the body vessel. Similarly, the sheath of the introducer generally has a proximally facing opening and a surrounding edge. If the sheath is advanced to meet the distally facing capsule, the edge of the sheath may engage with stents of the just introduced stent graft and dislodge the stent graft from its position on the wall of the body vessel. It is desirable to engage the sheath with the capsule before withdrawal. Therefore, it also is desirable to prevent the edges of the capsule and the sheath from dislodging the stent graft when the sheath and the capsule are brought into engagement.
Additionally, operation of the introducer may require manipulation of multiple trigger wires in a specified order. This may add to the complexity of the introducer. Such trigger wires also may add to the overall diameter or profile of the introducer. It is desirable, therefore, to reduce the number of trigger wires required to operate an introducer.